Lepton scattering from the proton and nuclei provides snapshots of their structure. In the
Standard Model, this structure is described by Quantum Chromodynamics in terms of quarks
and gluons. A major goal of present and future nuclear physics is to understand quantitatively
and comprehensively the structure of nuclei in terms of QCD. Ongoing, frontier studies using
the CLAS12 spectrometer at Jefferson Lab will be described. New targets and ion sources of
polarized He-3 are under development and will be discussed. Finally, the future Electron-Ion
Collider will be introduced.